A Simulator Study of TKR Kinematics Using Modeled Soft-Tissue Constraint: Virtual Soft-Tissue Control for Knee Simulation

The clinical relevance of knee simulation relies on the accurate reproduction of in vivo TKR kinematics. Current generation force-control knee simulators use mechanical springs to simulate the knee's soft-tissue constraint. Because the constraint provided by the soft tissue is complex in nature, with nonlinear force displacement characteristics and axis coupled behavior, it is difficult or impossible to model this behavior with mechanical springs. This paper describes a virtual soft-tissue control methodology, which provides enhanced modeling of the knee's soft tissue. TKR kinematics were evaluated for a posteriorly stabilized prosthetic device using a range of plausible soft-tissue models derived from the literature. The device was exercised with the standard ISO force-control waveforms while varying the constraint model to compare several different soft-tissue models. Kinematic and kinetic data were taken and tracking performance analyzed for several different constraint models.